TM 1-1520-240-103-3-22 (7)Observe the CDU display. The display indi-cated the GPS test mode status as of one of the follow-ing.GPS TEST: IN PROCESSGPS TEST: NOT RUNGPS TEST: PASSEDGPS TEST: FAILEDg. Procedure for Displaying GPS Key and GPSSpace Vehicle Status.(1)Set the DISPLAY switch to XTK/TKE/KEY.(2)Set the MODE switch to LAT/LONG (MGRSmay also be used).(3)The display indicates GPS daily key status,time remaining on the currently entered keys and howmany Space Vehicles (SV) are currently being used bythe GPS.KEYSTATUSTIMEREMARKSDKOKDays or hours stillavailable on keyGPS daily keyin use andverified.DKNO*No GPS dailykey availableDKIN*GPS daily keyavailable butnot verified.3-3-50. Preflight Procedures.a. Data Required Prior to DGNS Turn-onThe following initial data must be entered by the pilot aftersystem turn-on and initialization, unless previously en-tered data is satisfactory:Datums of operation, when using MGRS coordinates.This data may be part of the data load if preprogrammed.In combined or GPS mode the GPS provides preset posi-tion. If Doppler only mode is selected MGRS coordinatesof present position - zone area, easting and northing;latitude/longitude coordinates may also be used to inputpresent position. This data may be part of the data loadif preprogrammed. Variation of present position to thenearest one-tenth of a degree.Coordinates of desired destinations 00 through 99. It isnot necessary to enter all destinations in the same coor-dinate system. This data may be part of the data load ifpreprogrammed.Variation of destinations to the nearest one-tenth of adegree.Crypto-Key variables necessary to enable the GPS re-ceiver to operate in Y code are entered via remote fill dataonly and not via the CDU keyboard.NOTEDestinations are entered manually whensteering information is required to a destina-tion that was not in the set of data loaded viathe data loader, or it is desired to update pres-ent position by overflying a destination, or apresent position variation computation is de-sired. (See CDU operation). If a present posi-tion variation update is desired, destinationvariation must be entered. The operator mayenter one or more destination variations; it isnot necessary for all destinations to have as-sociated variations entered and also not nec-essary to enter all destinations in any case,but variations must be entered AFTER des-tination coordinates are entered.The Doppler outputs true heading and accepts magneticheading from gyromagnetic heading reference. If accu-rate magnetic variations are not applied, then navigationaccuracy will be affected.b. System Initialization(1)Enter GPS mode M.NOTEYou must select GPS mode M during initial-ization. If Y mode is selected before Crypto-Key variables are loaded the system will lock-up forever.You must select GPS mode M during initial-ization. If Y mode is selected before Crypto-Key variables are loaded the system will lock-up forever.(2)Perform self test (para d. below).(3)Perform download (para c. below) of dataloader cartridge if necessary, or manually enter datum,destinations, magnetic variations, and present position(para. f or g. below).(4)Load Crypto-Key variables (unless pre-viously loaded and still valid) necessary for operation ofthe GPS in Y mode.NOTEIt is necessary to wait at least 12 minutes forkey validation when new keys have been en-tered, or collection of almanac data when sethas no previous almanac data. During thistime the GPS operating mode must be M anduninterrupted. After this time the GPS operat-ing mode may be switched to Y. Observe theGPS Key status and number of SVs trackedafter switching to Y mode. If the SV numbergoes to zero repeat this procedure. The Keystatus shall switch from DK IN to DK OKsometime during the 12 minutes.(5)Check datum of operation, if MGRS is beingused.